MediumDD15

SPN 513 FMI 2 Detroit Diesel DD15 — Actual Engine Per (2026)

SPN 513 FMI 2 on Detroit Diesel DD15 means actual engine - percent torque - data erratic, intermittent, or incorrect. 60–80% of field cases trace to erratic engine speed sensor signal. Shop repair with parts runs $60 - $500; DIY wiring or filter work starts at $40–$150. Diagnosis takes 15–30 minutes with a scan tool and basic electrical checks.

What This Code Means

SPN 513 FMI 2 on Detroit Diesel DD15 tells the ECM that actual engine percent torque is outside calibrated limits. On J1939, FMI 2 specifies the failure mode: Actual Engine - Percent Torque - Data Erratic, Intermittent, Or Incorrect. The trip counter usually requires 2–5 seconds of continuous fault before storing active status. Actual engine percent torque isn’t measured by a single sensor - it’s calculated from engine speed, fuel rate, and rail pressure data. That means SPN 513 FMI 2 is really a symptom pointing back to one of those upstream inputs rather than a standalone fault to chase directly. ProfessionalDieselRepair.com works this one systematically, checking the engine speed sensor and fuel rate stability before assuming anything deeper is wrong, since those two inputs cause the overwhelming majority of erratic torque calculation faults.

Common Symptoms

• Inconsistent power delivery that’s hard for the driver to describe precisely (100% of cases)
• Amber Check Engine lamp (80% of cases)
• Torque values that jump or spike unexpectedly on the scan tool’s live data screen (60% of cases)
• Possible interaction with transmission shift quality on automated manual transmissions that use torque data for shift timing (40% of cases)

Likely Causes (Ranked by Probability)

1. Erratic engine speed sensor signal (45% of cases) — Since RPM is a core input to the torque calculation, an intermittent or noisy speed sensor signal directly corrupts the resulting torque value.

2. Unstable fuel rate or rail pressure sensor data (25% of cases) — Fuel rate and rail pressure feed the torque calculation; inconsistency in either input produces the same erratic torque symptom.

3. Loose or corroded ECM connector pins on input circuits (15% of cases) — A poor connection on any contributing sensor circuit can introduce noise that shows up as erratic calculated torque rather than a clean sensor fault.

4. J1939 network data corruption between modules (10% of cases) — If torque data is shared across the network with a transmission or other module, communication errors can occasionally produce erratic readings without a physical sensor fault.

Step-by-Step Diagnostic Guide

1. Pull the fault with DDDL and confirm SPN 513 FMI 2 is active; check for any accompanying faults on fuel rate (SPN 183), engine speed (SPN 190), or rail pressure sensors that feed the torque calculation. — Tool: scan tool or multimeter. Document readings on the work order.

2. Inspect the engine speed sensor and its wiring for looseness or damage, since an erratic RPM signal directly corrupts the torque calculation. — Tool: scan tool or multimeter. Document readings on the work order.

3. Check fuel rail pressure sensor readings for stability using DDDL live data - an erratic pressure signal will similarly throw off the calculated torque value. — Tool: scan tool or multimeter. Document readings on the work order.

4. Verify all ECM connector pins related to these input sensors are clean, dry, and fully seated. — Tool: scan tool or multimeter. Document readings on the work order.

5. If a transmission is present that shares this data over the J1939 network, check for any network communication fault codes that might indicate a broader data integrity issue rather than a single sensor. — Tool: scan tool or multimeter. Document readings on the work order.

6. Clear the code and road test while monitoring live torque data for stability across varying loads before returning the truck to service. — Tool: scan tool or multimeter. Document readings on the work order.

Repair Options (with Costs)

Repair	DIY	Independent Shop	Dealer
Actual Engine Percent Torque wiring repair	$25–$150	$150–$350	$250–$500
Actual Engine Percent Torque sensor/part	$60 - $500	$$60 - $500 + labor	$450+
Full module replacement	N/A	$600–$1,500	$450+

Platform-Specific Notes

On Detroit Diesel DD15, this code follows OEM J1939 diagnostic logic. Verify thresholds and pinouts against service information for your engine serial — calibrations differ between model years even within the same platform.

When This Code Sets

SPN 513 FMI 2 sets when actual engine percent torque fails the J1939 rationality monitor for a calibrated trip counter — usually 2–5 seconds continuous on electrical faults, longer on efficiency monitors. Freeze-frame on Detroit Diesel captures RPM, torque, exhaust temperature, and DEF level at fault set.

Scan Tool Parameters to Log

• Actual Engine Percent Torque live data PID at idle, cruise, and full load
• Battery voltage and ECM supply voltage
• Related aftertreatment and protection PIDs (SPN 1569 if stacked)

Common Misdiagnoses

Searching for a dedicated ‘torque sensor’ to replace — Techs unfamiliar with how this parameter is derived assume there’s a physical sensor for it, leading to a wasted parts search or an unnecessary parts-cannon purchase of the wrong component.. Instead: Recognize that this is a calculated value and diagnose the actual contributing sensors - engine speed and fuel rate - instead.

Replacing the ECM for an erratic calculation fault — When no single sensor jumps out as clearly faulty, some techs escalate straight to the control module.. Instead: Thoroughly rule out engine speed sensor and fuel rate/rail pressure sensor issues, plus connector integrity, before ever considering ECM replacement.

Shop Notes from the Field

Shop tip: because this is a calculated value, don’t waste time looking for a ‘torque sensor’ that doesn’t exist. ProfessionalDieselRepair.com works this fault by checking every input that feeds the calculation - engine speed, fuel rate, and rail pressure - rather than treating it as a single-component repair.

Safety Warning

• Use proper lockout procedures before working on any rotating components near the engine speed sensor.
• Disconnect the battery before repairing wiring near the crankshaft or camshaft sensor area.

Prevention Tips

• Inspect the engine speed sensor and its wiring at every major PM interval.
• Keep fuel system components maintained to avoid rail pressure instability that can cascade into torque calculation faults.
• Address any connector corrosion on input sensor circuits promptly.

Detroit Diesel Field Notes for SPN 513 FMI 2

• Compare this unit’s repair history: repeat SPN 513 FMI 2 within 5,000 miles indicates incomplete prior repair, not a new component failure.
• If actual engine percent torque was recently replaced, verify correct part number for engine serial — superseded calibrations require matching hardware revision on Detroit Diesel.
• Capture a 20-minute data log of actual engine percent torque parameter during mixed driving before closing the work order — intermittent FMI signatures need road replication, not bay-idle checks.
• Check for OEM technical service bulletins covering SPN 513 FMI 2 on DD15 — many bulletin fixes address harness routing rather than sensor replacement.
• Torque actual engine percent torque mounting fasteners per Detroit Diesel OEM spec — verify with engine serial. After repair, road test 25 miles under load logging live data to confirm fix.
• Document ambient temperature and key-cycle count at fault set on Detroit Diesel DD15 — cold-soak faults on actual engine percent torque often clear after warm-up when moisture is the root cause.

Related Codes

• SPN 190 FMI 8 — often stacks with SPN 513 FMI 2
• SPN 512 FMI 2 — often stacks with SPN 513 FMI 2
• SPN 183 FMI 2 — often stacks with SPN 513 FMI 2

FAQ

Can I drive with SPN 513 FMI 2 active?

Yes, though expect inconsistent power delivery. If the truck has an automated transmission, shift quality may also be affected since some AMTs use torque data for shift timing.

Is there a dedicated torque sensor I need to replace?

No - actual engine torque is a calculated value derived from engine speed, fuel rate, and rail pressure data, not measured by a single physical sensor.

How do I reset SPN 513 FMI 2 without a scan tool?

You need DDDL or a comparable diagnostic tool to clear the stored fault once the underlying sensor input causing the erratic calculation is repaired.

What does SPN 513 FMI 2 mean on Detroit Diesel DD15?

SPN 513 FMI 2 means actual engine - percent torque - data erratic, intermittent, or incorrect. The ECM detected actual engine percent torque outside calibrated limits. Verify with freeze-frame data before clearing.

Can I drive with SPN 513 FMI 2 active?

Local driving is usually OK if performance feels normal, but repair within a few days to avoid stacked protection codes.

How much does it cost to fix SPN 513 FMI 2?

DIY repairs start at $40–$150 for wiring or filters. Shop repairs with parts run $60 - $500. Dealer pricing runs $450+.

What is the most common cause of SPN 513 FMI 2?

Erratic engine speed sensor signal — confirm with visual inspection and live data before ordering parts.

Sources

• SAE J1939-71 — SPN 513 parameter definition
• Detroit Diesel OEM service information — verify by engine serial
• Mitchell1 ProDemand — 2026 labor and parts cost surveys

Related Reading

• Detroit Diesel fault codes hub
• Diesel repair cost estimator
• Actual Engine Percent Torque diagnostic guide
• SPN 190 FMI 8
• SPN 512 FMI 2